The present invention relates to an epitaxy method for semiconductor crystals. And more particularly to an epitaxy process for a Group III-V compound semiconductor layer on a substrate consisting of a material which has a lattice constant and thermal expansion coefficient differing from those of the Group III-V compound that constitutes the grown crystal material.
Group III-V compound semiconductors, such as gallium nitride (GaN) semiconductors, have attracted attention as materials for blue light-emitting devices due to their wide (3.4 eV) energy band gap or forbidden band gap and to the fact that they are direct-gap semiconductors.
The substrate material used in fabricating a light-emitting device with a Group III-V compound material is preferably a single crystal of the same material used for growing the epitaxial layer. With crystals such as GaN, however, the production of bulk crystal is difficult due to the high nitrogen dissociation pressure. Thus, when fabricating light-emitting devices or the like using GaN or other materials for which production of bulk crystal is difficult, the practice has been to fabricate various devices using a sapphire (Al2O3) substrate or the like. However, sapphire (Al2O3) substrates differ completely from Group III-V compounds in terms of lattice constant, thermal expansion coefficient, and other physical properties, as well as in terms of chemical properties.
When the physical properties, such as lattice constant and thermal expansion coefficient, and the chemical properties of a substrate differ completely from those of the material which is to be grown to produce the compound semiconductor layer, the following problems can arise. Fabrication of materials in which the substance used for epitaxy differs from the substance of which the substrate consists (hetero substrate) reportedly has problems in terms of epitaxial layer strain, lattice defects, and the like, particularly the occurrence of cracks when it is attempted to grow a thick crystal film (Japanese Journal of Applied Physics, Vol. 32, 1993, p 1528-1533). In such cases, not only is device performance severely impaired, but damage to grown crystal films due to internal stress is not uncommon.
The following has been proposed as a way of obtaining a high-quality epitaxial layer with a low dislocation density in lattice misfit epitaxy processes. Japanese Laid-Open Patent Application 8-64791 teaches the formation of an SiO2 oxide film layer of stripe form approximately 1 xcexcm wide on the sapphire substrate prior to growing the Group III-V compound. This is followed by epitaxy of a GaN film on the sapphire substrate, causing lattice defects and dislocations to become concentrated in a designated area of the substrate. In the example given in Japanese Laid-Open Patent Application 8-64791, GaN film growth does not occur in the SiO2 film areas on the sapphire substrate, making it impossible to form an epitaxial layer over the entire surface of the epitaxial layer, making it difficult to produce a device.
It is an object of the present invention to provide a formation method whereby creation of strain and defects in the substrate and epitaxial layer are minimized, even during epitaxy conducted using a hetero substrate which has a different lattice constant and thermal expansion coefficient, and which affords an epitaxial layer that resists cracking even where a thick film is grown.
In order to achieve the aforementioned object, the Group III-V compound semiconductor manufacturing method employing epitaxy which pertains to the present invention comprises a step in which growing areas are produced using a mask patterned on a semiconductor substrate surface; a step in which Group III-V compound semiconductor having a lattice constant and thermal expansion coefficient different from those of the substrate is grown in the growing areas; and a step in which the Group III-V compound semiconductor is grown in the growing areas while forming facet structures, covering the mask material together with the Group III-V compound semiconductor in the adjacent growing areas, and the facet structures are then buried to planarize the surface.
The method for manufacturing a Group III-V compound semiconductor which pertains to the present invention comprises, in a Group III-V compound semiconductor layer epitaxy process, a step wherein growing areas are produced using a mask patterned on a semiconductor substrate surface; a step in which Group III-V compound semiconductor having a lattice constant and thermal expansion coefficient different from those of the substrate is grown in the growing areas; and a step in which the Group III-V compound semiconductor is grown in the growing areas while forming facet structures, covering the mask material together with the Group III-V compound semiconductor in the adjacent growing areas, and the facet structures are then buried to planarize the surface, the above steps being conducted repeatedly on the planarized surface.
The method for manufacturing a Group III-V compound semiconductor which pertains to the present invention further involves forming a Group III-V compound semiconductor film 12 consisting of the same material as the Group III-V compound semiconductor layer grown in the growing areas, or one having a similar lattice constant and thermal expansion coefficient, and then forming growing areas formed by a patterned mask material. The growing areas produced using the mask material are of a stripe, rectangular, round, or triangular configuration.